Automotive parts, such as wire harnesses for connecting a number of electric devices mounted on an automotive vehicle, are typically routed through crowded engine compartments that reach temperatures ranging from -40.degree. C. to 200.degree. C. The insulated wires that make up these wire harnesses are not only exposed to this expansive and fluctuating temperature range but are also exposed to water and possibly to flames and corrosive fluids that have the potential to erode, swell or otherwise degrade the insulation that covers these wires. Therefore, the insulation, by necessity, has to demonstrate strength and toughness, flame and corrosion resistance and resistance to hydrolysis and thermal degradation.
Trends in the automotive industry have resulted in increases in the number of electrical devices mounted on an automotive vehicle in addition to reductions in the size of engine compartments. As a result, weight and volume restrictions have been placed upon the components that are housed in the engine compartments. In specific regard to automotive electrical harnesses, restrictions as to the thickness of the insulating coating on the wires that make up the electrical harnesses have been required by the automotive industry.
The insulated wires that are currently used in electrical harnesses typically employ a polyvinyl chloride (PVC) insulating coating having a wall thickness of about 0.40 mm. While these PVC insulated wires satisfy minimum performance requirements set by the automotive industry when exposed to temperatures up to about 105.degree. C., deterioration of the insulating coating's physical and mechanical properties has been noted when these insulated wires are exposed to temperatures exceeding 105.degree. C.
Current specifications from auto makers now require ultra thin wall harness wire having insulation wall thicknesses of 0.25 mm or 0.1 5 mm. However, at such thicknesses the drawbacks or problems associated with PVC insulated wires would render ultra thin wall PVC insulated wires unsuitable for the above-referenced automotive applications.
It is well known that polyamicles in general use today such as nylon 6, nylon 6,6 and the various copolymere desirable for most applications. However, their desirability diminishes for specialty applications such as electrical insulation of automotive parts which, as alluded to above, require exceptional physical, mechanical, electrical and thermal properties. In particular, nylons are degraded by hydrolysis at elevated temperatures and, to a certain degree, are degraded by strong acids. Good mechanical properties are maintained only up to about 125.degree. C.
The prior art describes various techniques for modifying polyamides with tougheners. Such tougheners include low modulus ethylene copolymers that contain carboxyl or anhydride functionality. Other tougheners include ethylene acid copolymers neutralized with metal cations. (See U.S. Pat. No. 5,126,407 to Subramanian).
Combinations of polyamides with such tougheners afford compositions that are tough and suitable for injection molding and extrusion yet still unsuitable for the above-referenced electrical applications. In particular, such combinations continue to render compositions that lack the necessary resistance to hydrolysis and strong acids especially at elevated temperatures and under humid conditions.
Accordingly, there is a need for harness wire and especially ultra thin wall harness wire that overcomes the drawbacks associated with the prior art and that demonstrates strength, toughness and a balance of resistance properties.
It is therefore an object of the present invention to provide a thermoplastic coating composition that can be used as an insulating coating for wire and that demonstrates strength, toughness and a balance of resistance properties.
It is a more particular object to provide an insulating coating composition for wire that, when applied at coating thicknesses of less than or equal to 0.25 mm or 0.15 mm, demonstrates strength, toughness and a balance of resistance properties.
It is a further object of the present invention to provide an ultra thin wall insulated wire product that demonstrates the above-referenced properties.
It is yet a further object to provide an insulated conductor made up of a plurality of ultra thin wall insulated wires that each demonstrate the above-referenced properties.